For the production of hydrocarbons from a well bore after the borehole is drilled, it is lined with a casing which is cemented in place to prevent fluid migration along the annulus between the casing and well bore. The interior of the casing is placed into fluid communication with the earth formations bearing the hydrocarbons under pressure by means of perforations which extend through the casing, the cement sheath and into the earth formations. The perforations are typically produced by a shaped charge gun which is lowered to the desired depth of the desired perforations while the bore to the earth's surface is filled with fluid which creates a hydrostatic pressure at the location for the perforation where the hydrostatic pressure is greater than the expected pressure of the hydrocarbons in the formations. Thus, when the perforations are produced in the formations, the pressure of the hydrocarbons is controlled by the greater pressure of the fluid in the bore. In the development of perforations by using shaped charges it has been established that a certain amount of metallic debris from the shaped charge invades the perforation and that the wall surface of a perforation is affected so as to reduce or adversely affect its permeability or ability to pass fluid. Thus, when the pressure differential is reversed by reducing the pressure in the bore, the fluid flow from the formations is not as significant as it might be in the absence of debris in the perforation or damage to the surface wall of the perforation. There are a large number of existing wells which were completed before this knowledge was available. It is thus desirable to revitalize older wells as well as wells currently being developed.
It is to the foregoing problems that the present invention is addressed. Previous efforts to solve these problems have included a number of approaches and, where the pressure differential across the perforation can be suddenly reversed, the attendant shock can act to unblock or "clean out" a perforation. Previous devices and systems for accomplishing this result have a number of drawbacks, the principal drawback being that an entirely separate operation is required from the completion operation and this typically involves substantial additional cost and risk in obtaining production from the well. By means of the present invention, the well can be set up for completion with a tubing and packer and the perforations are made. Thereafter, by use of the tool of the present invention, the perforations in the well can be easily cleaned up using a wire line which is an inexpensive and easy to accomplish operation.